ABSTRACT
In river floodplains, vegetation zonation is strongly influenced by water-level fluctuations. Depending on elevation level and flood intensity, a natural as well as a human-influenced environmental gradient can be observed. The natural vegetation consists of softwood and hardwood forests. Grazed marsh and grassland are the characteristic communities of agriculturally used floodplains. Individual plants occurring in floodplains must develop adaptive mechanisms in order to survive transient floods. These mechanisms are discussed at the level of life history strategies and at the physiological level in relation to the position of the species in the floodplain gradient.
Species from the higher sites favor rapid germination after seed release while species from lower sites postpone germination or survive in the vegetative stage as a response to flooding. Flood-tolerant species are able to form aerenchymatous roots and survive submergence by their ability to accelerate shoot extension which restores leaf-air contact. Phytohormones, especially ethylene, play an important role in the adaptive responses to flooding.
The study of adaptive mechanisms of species occurring along the floodplain gradient will result in a better understanding of flooding-related processes acting at the community level.
